Recent flooding in the Red River Valley has threatened northern Midwest cities such as Fargo, North Dakota and its neighboring city Moorhead, Minnesota. Both of these cities are located well withing the Red River's flood plain making them forever vulnerable to flood hazards. The geology and geography of the Red River Valley are key factors in creating flood events.
Red River Valley is Flood-Prone
There are four main reasons for flooding in the Red River Valley:
- The Red River flows north, so it flows in the direction of warming temperatures and melting snow. This can cause a build-up of melt waters and result in a swollen river, especially in northern areas along the river.
- Chunks of ice also flow north with the Red River. Ice jams in northern areas of the Red River can inhibit flow and raise river levels.
- The Red River Valley is very young and carves through one of the flattest areas in the world – an ancient lake bed leftover from Glacial Lake Agassiz. The Red River itself is only 9,300 years old; far too young to have carved out a proper valley.
- The gradient, or slope, of the Red River decreases as it flows north, so the speed of the river also decreases, increasing the risk for pooling to occur as the river naturally spreads out to form a lake.
Precipitation is not listed as one of these main reasons. This is because, unlike many other rivers in the United States, the effects of the valley geography and topography play a much greater role in the chances of flooding than does precipitation. However, a high amount of precipitation during the fall, winter and spring months can definitely exacerbate the situation.
Geology Induced Hazards in the Valley
Geologist Donald P. Schwert of North Dakota State University has written a report of the Red River Valley in a document titled "A Geologist's Perspective on the Red River of the North: History, Geography and Planning/Management Issues." In this document, Schwert addresses three issues that play a large role in the Red River's impact as a hazard to communities.
One of these issues is mass wasting along the Red River, which is a common geologic process that occurs with most meandering rivers, like the Red River. Meandering rivers snake through the terrain, forming cut-banks along the outer edges of the river where the water is traveling at faster speeds. Because the water is traveling at a higher velocity as it flows along the outer cut-banks, more erosion occurs, carving out the banks more and more. The result can be mass wasting that threatens the stability of river banks along with any commercial or residential development along these banks.
Another issue is flooding along the Red River. The young age of the river has produced a river valley that is very flat. As soon as the river flows over its banks, the water spreads out over the plains very easily and broadly. However, the more the river floods, the more it is able to carve out a proper valley by increasing water flow and erosion. Residential and commercial development along the Red River has impacted this process by eliminating natural storage and obstructing natural flow. Eliminating natural storage causes more flooding upstream because of the displacement of water. Likewise, the placement of low bridges over the river creates areas for ice and trees to get stuck, increasing the risk from flooding upstream.
The final issue discussed by Schwert is how to accommodate both the Red River and human settlement in the valley. For this Schwert offers a quote used in his geology courses at NDSU, "Often the most efficient approach to resolving a geologic problem is to avoid the problem altogether." With this advice, Schwert volunteers suggestions for how humans can reside in the Red River Valley with less vulnerability. These relate mostly to new construction and mention banning basements, since these are the first to flood, and forcing buildings to be constructed on a thick platform of well-drained aggregate.
Related Articles:
Source:
Geology of the Fargo/Moorhead Region - North Dakota State University
 |
 |
 |
